This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Mechanical loading may be the most important external factor regulating the development and maintenance of cartilage. Cellular perception of mechanical stress within cartilage is an important modulator of cartilage cells (chondrocytes) function, including the induction of gene expression, cell growth and differentiation. MicroRNAs (miRNAs) are small noncoding gene products that play an important regulatory role in determining cell function. The first aim of our study is to investigate whether miRNAs contribute to converting mechanical information into the molecular events in chondrocytes. The second aim of our study is to define how miRNAs regulate this process that controls chondroctye function. By using a unique 3D chondrocytes culture loading system in conjunction with the miRNA array, we have identified miR-365 as an important regulator of chondrocyte function in mechanotransduction pathways. MiR-365 significantly stimulates cartilage cell proliferation and differentiation. Furthermore, we also provide the underlying mechanism by which miR-365 regulates chondrocyte function through histone deacetylase 4 (HDAC4), an inhibitor of chondrocyte maturation, and thereby regulating its downstream effectors. Collectively, our study has shown for the first time that mechanical stress regulates the chondrocyte function through miR-365. These findings not only provide new insights into mechanotransduction signaling pathways, but also raising intriguing possibilities of using miRNA for modulating cartilage tissue engineering in regenerative medicine.